Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.52   3.139%   $191.3435   $191.34   $191.35   $191.30  
  Purchase #2 $191.84   3.696%   $198.9304   $198.93   $198.95   $198.90  
  Purchase #3 $26.88   8.661%   $29.2081   $29.21   $29.20   $29.20  
  Purchase #4 $154.57   10.269%   $170.4428   $170.44   $170.45   $170.40  
  Purchase #5 $6.92   7.584%   $7.4448   $7.44   $7.45   $7.40  
  Purchase #6 $203.81   10.830%   $225.8826   $225.88   $225.90   $225.90  
  Purchase #7 $202.28   9.515%   $221.5269   $221.53   $221.55   $221.50  
  7 purchase totals = $971.82       $1,044.7791   $1,044.77   $1,044.85   $1,044.60